(TAMPA, Fla.) — Tampa police are investigating after a man allegedly admitted to killing his two roommates because he believes they disrespected his Muslim faith.

Devon Arthurs, 18, was arrested Friday and faces two counts of first-degree murder, two counts of aggravated assault and three counts of armed kidnapping.

Around 5:29 p.m. local time on May 19, Arthurs entered Green Planet Smoke Shop in Tampa armed with a black semiautomatic pistol, according to a police report on the incident. He allegedly demanded that the employee and one customer who were in the store at the time get on the ground as he pointed the gun at one of the captives.

“Why shouldn’t I kill you?” one victim says Arthurs yelled while holding them captive, according to the police report.

About two to three minutes after Arthurs entered the shop, a second customer entered and was also ordered to get on the ground.

“Arthurs informed all three victims in the store that he had already killed somebody,” said the police report. “He further informed all three victims that he was upset due to America bombing his Muslim countries.”

Approximately five minutes after the third victim entered the store, two Tampa police officers arrived to the scene and confronted Arthurs.

According to the police report, one victim was able to run away from the scene, while the officers convinced Arthurs to let the remaining two victims go. After minutes of negotiating, Arthurs surrendered and allowed officers to arrest him.

While being walked to the police car, Arthurs made references to “Allah Mohammed” and stated, “I had to do it. This wouldn’t have had to happen if your country didn’t bomb my country,” according to the police report.

While under arrest, Arthurs was asked if anyone else was hurt, to which he replied, “The people in the apartment, but they aren’t hurt, they’re dead,” according to the police report.

Arthurs then directed police to the apartment, where two male victims were found dead. He identified the victims to police as his roommates Jeremy Himmelman, 22, and Andrew Oneschuk,18, and provided details of the shooting, including the rifle he used, the sequence of events, and the exact location of the shooting and the placement of the shot on each victim, according to the police report.

Arthurs stated that he had once shared a common neo-Nazi belief with his two roommates before converting to Islam, and that the shooting deaths were caused by the individuals disrespecting his Muslim faith.

Arthurs’ fourth roommate, Brandon Russell, was also arrested May 21 after allegedly being linked to explosive devices found in the apartment.

When police arrived to the apartment where Himmelman and Oneschuk were found dead, Russell was seen outside of the apartment dressed in full U.S. Army camouflage “crying and visibly upset,” according to the police report.

“That’s my roommate (Russell),” Arthurs said, according to the report. “He doesn’t know what’s going on and just found them like you guys did.”

Arthurs also told police that before the murders he had been aware of “Russell participating in online neo-Nazi internet chat rooms where he threatened to kill people and bomb infrastructure,” according to the report.

“From our point of view, there was a double homicide and we arrested the guy who did the homicide,” a spokesperson for Tampa Police Department told ABC News. “When we started talking to him and got info about neo-Nazi and stuff in the apartment we called the FBI and we are certainly working with [them].”

Tampa police obtained a state search warrant for the apartment, where law enforcement discovered a cooler in the garage with a white, cake-like substance. Two FBI and Tampa Police Department bomb squad officials identified the substance as an explosive known as hexamethylene triperoxide diamine, according to a criminal report from the United States District Court for the Middle District of Florida.

Other bomb-making materials and firearms were also found in the apartment. Nazi and white supremacist propaganda were discovered in Russell’s bedroom, including a framed photo of Oklahoma City federal building bomber Timothy McVeigh.

Russell, who is associated with the Army National Guard, allegedly admitted to law enforcement officials that he was a national socialist, a neo-Nazi and a member of a self-organized group called “Atom Waffen,” which is German for atomic weapon, according to the criminal report. They say he also admitted to owning the explosive devices found in the garage, and said they were used to make homemade rockets in 2013 when he was in an engineering club at the University of South Florida.

Russell was arrested by the FBI on May 21 and is charged with possession of unregistered destructive device and unlawful storage of explosive material. It is unclear if he is represented by an attorney and has not been scheduled a court date yet.

Arthurs, who is represented by a public defender, has a hearing set for May 24 at 10 a.m. local time.